Electricity question again

West Cork Paul

West Cork Paul

Man in a Shed
Subscriber
Sorry I’ve been AWOL just been really busy. Anyway, I’ve a question for the likes of @Alan Williams or @AirCon or anyone else who knows about these things.

Reg/rec on a bike, it’s knackered, only putting out 3-4V. It’s got 40-50v AC going into it so it’s not the stator -this is an old 1995 Yamaha with a weedy generator, but what limits the current output from the r/r?

The reason I ask is because the in-line fuse from the r/r +ve output to the +ve terminal of the battery keeps blowing.

Am I right in thinking that if the wattage output of the stator is for eg 360W at full chat if that’s coming out of the stator at say 40v x 9A and going through the r/r and the r/r is only putting out 4v then the current must have surged to 90A?

There was some original wiring which had become burnt, I’m thinking it’s due to the excess current but want a sanity check.

BTW the r/r doesn’t get very hot at least nowhere near as hot as the wiring is/was getting.
 
Paul the genny should be outing more than 50VAC, engine should be running @ 3500rpms
Last time I replaced a stator, the new reading was 105VAC
Stator and RR sound like they need replacing, possible shorting/ earth problems too by the sound of it
 
So many issues here...

What limits voltage is the regulator.
Is it single, bi or three phase stator?
Are the resistances the same for each coil and is it sufficiently isolated from the chassis?

Are all the connections good, zero corrosion and no fractured cables?
Is the battery good, what is the voltage when disconnected from the bike for 24 hours?

The R/R, first provides voltage rectification (Ac to Dc), then smooths it (reducing the dc ripples).
It's final job is dissipation of excess energy into heat, thus ensuring the battery and bike electrical components don't fry.

It sounds like a damaged R/R, if it is being correctly fed... it could be the output semiconductors have punched through to earth and the battery reverse current is blowing the fuse.
 
Last edited:
BobTheBounder said:
Paul the genny should be outing more than 50VAC, engine should be running @ 3500rpms
Last time I replaced a stator, the new reading was 105VAC
Stator and RR sound like they need replacing, possible shorting/ earth problems too by the sound of it
Click to expand...
It’s a shitty old 1995 Yamaha XV535 Virago, they’re known for having low output stators apparently.
 
AirCon said:
So many issues here...

What limits voltage is the regulator.
Is it single, bi or three phase stator?
3 PHASE
Are the resistances the same for each coil YES and is it sufficiently isolated from the chassis? YES - both aspects checked.

Are all the connections good, zero corrosion and no fractured cables? THEY ARE NOW, I PUT IN NEW WIRING OVER THST SECTION
Is the battery good, what is the voltage when disconnected from the bike for 24 hours?
YES, 12.7v
The R/R, first provides voltage rectification (Ac to Dc), then smooths it (reducing the dc ripples).
It's final job is dissipation of excess energy into heat, thus ensuring the battery and bike electrical components don't fry.

It sounds like a damaged R/R, if it is being correctly fed... it could be the output semiconductors have punched through to earth and the battery reverse current is blowing the fuse.
Click to expand...

Answers inserted above 🙏

I like the last sentence that could very well be the reason. I have done forward & reverse bias diode tests on it - which it fails but haven’t checked whether there’s continuity from the r/r +ve output to earth. Anyway, that’s academic now as it’s certainly toast but it could be the explanation as to why the fuse keeps blowing and the wiring gets hot.
 
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